Contents lists available at ScienceDirect European Journal of Soil Biology journal homepage: www.elsevier.com/locate/ejsobi Pectin drives microbial phosphorus solubilization in soil: Evidence from isolation-based and community-scale approaches Kazumori Mise a,b,∗ ,YukiKoyama a , Arisa Matsumoto a , Kazuki Fujita c , Takashi Kunito c , Keishi Senoo a,d , Shigeto Otsuka a,d a Department of Applied Biological Chemistry, Graduate School of Agricultural and Life Sciences, The University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo, 113-8657, Japan b Department of Biological Sciences, Graduate School of Science, The University of Tokyo, 2-11-16 Yayoi, Bunkyo-ku, Tokyo, 113-0032, Japan c Department of Environmental Science, Faculty of Science, Shinshu University, Asahi, Matsumoto, 390-8621, Japan d Collaborative Research Institute for Innovative Microbiology, The University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo, 113-8657, Japan ARTICLEINFO Handling editor: Bryan Grifths Keywords: Soil microbes Phosphorus solubilization Pectin Phosphorus cycling Rhizosphere Phosphate-solubilizing bacteria ABSTRACT A considerable part of soil phosphorus is bound to metal cations or metal oxides, and cannot be used in these forms by soil microbes and plants. Phosphate-solubilizing bacteria (PSB) are abundant in pectin-rich rhizo- sphere,andtheirpectin-degradingactivityhasbeenreported.Therefore,wehypothesizedthatpectinactivates PSB and promotes soil phosphorus solubilization. To test this hypothesis, we frst tested the phosphate-solubi- lizingactivityofpectin-degradingbacteria.PSBweremorefrequentlyisolatedfrompectin-containingmedium, comparedwithothermedia(P < 0.001).Furtherinasoilmicrocosmexperiment,weexaminedwhetherpectin amendmentacceleratedsoilphosphatesolubilization.Pectinamendmentdecreasedtheconcentrationsoflabile metallophosphate but increased the content of microbial biomass phosphorus in soils, meaning that phosphate solubilization was promoted by pectin amendment. In addition, PSB-like clades of bacteria increased by up to three times in response to pectin addition. This indicated that pectin amendment encouraged proliferation of PSB,acceleratingsoilphosphorusturnoverprocessesinitiatedbysolubilizationofmetallophosphate.Inlinewith these results, genomic analysis indicated the widespread distribution of pectin-degrading genes among PSB, suggesting the possible co-evolution of pectin-degrading and phosphate solubilizing functions. 1. Introduction A considerable part of soil phosphorus is inorganic phosphorus combined with metal cations (metallophosphate) [1], which is solubi- lized by phosphate-solubilizing bacteria (PSB). They solubilize me- tallophosphate by secreting organic acids to acidify their surrounding environments. Phosphorus solubilized by PSB is basically incorporated into microbial biomass, followed by the release from lysed cells in the form of bioavailable orthophosphate. Thus, enhancing the activity or abundance of PSB would contribute to increased phosphorus avail- abilityinthesoil.Onehotspotofsoilphosphorusmobilizationisplant rhizosphere[2],whichischaracterizedbyadistinctenvironmentfrom the bulk soil fostered by a variety of root exudates. The efect of root exudate compounds (organic acids, sugars, and fatty acids) on soil microbeshasbeenintensivelyexplored:theyhavebeenshowntofavor specifckindsofmicrobesanddriveassemblyofrhizospheremicrobial communities [3,4],includingPSB[5,6]. Protection of plant root from physical damage [7] and/or alumi- nium toxicity [8,9] has been perceived as a role of root-secreted mu- cilage.Themajorcomponentofplantrootmucilageispectin[10]that isthoughttobeoneofthemainrootexudates[11].However,theefect of pectin on soil PSB is far less well understood. Interestingly, past studiesfocusingonculturedPSBstrainsreportedthatahighproportion of PSB strains presented pectinase activities [12,13]. In addition, pectin-degradingbacteriawerefrequentlyisolatedfromsoilsharboring largenumberofphosphatesolubilizingmicrobes(includingPSB)[14]. These may imply that the activity or abundance of PSB in soil is en- hanced by pectin; from these studies, however, it is not clear whether PSBproliferateundertheexistenceofpectin.Inaddition,itispossible thatmicrobesinsoilcouldpresentfunctionalitiesinconsistenttothose observedonagarplates,meaningthattheabove-mentionedhypothesis mustbetestedinactualsoil. https://doi.org/10.1016/j.ejsobi.2020.103169 Received31July2019;Receivedinrevisedform28January2020;Accepted3February2020 ∗ Corresponding author. Department of Applied Biological Chemistry, Graduate School of Agricultural and Life Sciences, The University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo, 113-8657, Japan. E-mail address: mise-33@bs.s.u-tokyo.ac.jp (K. Mise). European Journal of Soil Biology 97 (2020) 103169 1164-5563/ © 2020 Elsevier Masson SAS. All rights reserved. T